This invention relates to an exhaust brake unit which is generally inserted into exhaust pipe connections of automobiles so as to effect an auxiliary braking system by closing an exhaust gas passage.
Different types of exhaust brake units are already known. In a first type, a gate valve slides vertically to the direction of an exhaust gas flow. In a second type, a butterfly plate or a flap is provided with an exhaust gas passage, swinging to open and close the passage. In the latter type, there is a disadvantage in that the valve member and its hinge portion are liable to be damaged or destroyed because they are directly exposed to the heat of the exhaust gas. Another disadvantage is that while the valve member is held at an open position in a normal driving mode, it causes considerable flow resistance against the exhaust gas flow, which has a bad influence upon the driving speed.
In Japanese Utility Model Publication No. 301986/84 issued on Aug. 29, 1984, there is disclosed an exhaust brake unit in which a cavity is formed inside a case parallel to the direction of the exhaust gas flow, a hinge being located at an end of the cavity, a flap-type valve member being mounted on the hinge and swinging thereon, so that the valve member is adapted to open and close the exhaust gas passage. In this design, during the closing stroke the single flap should swing upon the hinge against the direction of the exhaust gas flow, overcoming the exhaust gas pressure so as to shut-off the exhaust passage. The hinge and a shaft for the flap are thus subjected to great stress, and as a are worn out within a relatively short period and have poor durability. Moreover, since a large force is needed to move the flap toward the closing direction, the dimensions of the actuating means such as a cylinder or a vacuum diaphragm become large and an accommodation space for the exhaust brake unit also becomes large. Thus, the production cost is increased.
Some types of the exhaust brake units have another problem in that a complete shut-off is not effected, giving a poor braking performance.